Milling isobutylene-multiolefin copolymer synthetic rubber prior to curing



Patented Jan. 17, 1956 UNITED STATES PATENT OFFICE =MILLIN G .ISOBUEYLENE -MULTIOLEFIN' CO- POLYMEB SYNTHE'JJIC RUBBER PRIOR TO CURING IrvingE. Ligh'tbown, Westfield; N.:J., andWilliam alflparksandflobert M. Thomas, Baton Rouge, ;La., assignors, by mesneassignments, to Jason, :Incorporated, a corporation of Louisiana 'No Drawing. ApplicationDecember 17, 1947,

Serial. No. 792,334

,7tClaims.

This invention :relates :to ::.the processing wof synthetic curable z copolymeric v,elastomers; re-

lates particularly tuna processingrtreatmentifor increasing the tensile strength and :homogeneity of such polymers; andirelates especiallyztoxthe stepof applying ta heavy mechanical working at elevated temperatures to improve itheicuring properties of curable, low iodine number, .olefinic, synthetic polymers.

It has'beenfound possible, by a lowttempera ture treatment with a: catalyst, to. producetolefinic copolymers or interpolymers :which are strongly rubbery in character. Theseelastomerlc copolymers are composed of"substantialiamounts ocymene, 2 methyl 3 monyl butadiene-1;3;and the like. These polymers are prepared at temperatures rangingfrom -'40 Csto l03 C: or "lower to temperatures as low as 164 C. by the application to the mixed polymers of adissolved active metal halide catalyst or Frledel-Crafts type catalyst, such as aluminum "chlorideinsolution in an apropriate low freezing'inei't' solvent. Theseinterpolymers are susceptibletoa curing treatment with such substances as sulfur in the "presence of certain sulfur compounds, ordnthe"; presence of organic compounds which contains. quinonoid nucleus of the benzene or naphthalene-series. However, difficulty has been encounteredin the curing step because of a tendency on the part-of the interpolymeric materials to develop" bubbles or'blisters of flaws within thebodyof thematerial during the forming and curing operations, which difficulties markedly and seriously reduces the tensile strength of the cured material.

It is now found that if the material as received fromthe polymerizing process is subjected to a severe mechanical working or masticating ,a milling treatment at an, elevated temperature for'a substantial period of time, the tendency to" form blisters, flaws, bubbles and weakspots in the material in subsequent operations is removed and a very substantial improvement in tensile strength, elongation, and flexure and abrasion resistance-is obtained. The reason for this improvement is at the present time wholly unknown "and no proof of the character of thereaction presumably ,2 occurring ,in the, material during the heavy-milling, treatment has beenobtained. However, it iswsuggested and it. may be, that; during thehot working treatment, some interfering substance is removed. This substance, maybe traces :of low polymerswwhichshave 1 a boiling point below the curing temperature, these low polymers being removed either by volatilization or by .further polymerizatiomror itmay be that minute traces ofwwater; are, removed; or;=it maybe that catalyst residues or complexes produced in the, reaction are either :driven out or neutralized. The elimination 1 .or neutralization of such :constituents i has been found to have a marked eifecton the character, of the ultimate product; ingparticular, having a profound influenceupon the ease and emvciency of extrudingan'd uponthevcharacteruof the .curingrreaction,asince the untreated polymer shows bad blistering both during. extrusionwand under the heat incident to the curing step. ,Z'Il'le blistering takes the form ;of,a very large number ofblisters of: a wide range of sizes ;1 each :blister yielding. a discontinuity inxtheubody of the; material, thereby greatly reducing the tensile strength. This loss in properties is found; to .00-

cur with all of the varioustypesof low-unsaturation copolymers and with all of thevariouacuring agents which are mused 1 with 1 these :copolymers. The processing treatmentis preferably conducted in a Banbury type oflmillatra temperature between 150 C. and 200 C.:fora period ranging from about 5 to about 30 minutes. Alternatively, however, the processing maycbe conducted ,upon

a double roll mill, again at a temperatureiwithin the same range and for a similar length ofwtime, or in analogous masticating equipment which will produce heavy working pressuresat high temperatures.

Thus an object ofthe invention is totreat a hydrocarbon copolymer material by the application thereto of a drastic milling process .at an elevated temperature for a prolonged period, as a preliminary to adding curing ingredients eX- trudingand curing the copolymer for the production of amaterial having high tensilestrength, high elasticity and substantial uniformity througout the body of the material and for the increase of the flexureand-abrasionresistance as Well as suitability for blending Withother polymaterials. Other objects anddetails of the invention will be apparent from the followingdescription.

Broadly, this invention appliesto the treatment of olefi-nicinterpolymeric materials by an operation of severe --milli-ng and heating, of"a intent will yield blisters in it.

3 character not tolerated by other rubber-like substances, such as caoutchouc. This treatment has been found to yield a very substantial improvement in the physical characteristics of the polymer material, and it is in sharp contrast to the treatment applied to other rubbers, which are rapidly broken down into lower molecular weight substances or converted to insoluble resinous materials by such high temperature treatment. For this reason the uniform practice with rubber and other rubber-like materials has been to subject them to a minimum amount of milling, at the lowest temperatures for the shortest possible times and at the lowest pressures consistent with the obtaining of the desired plastic and homogeneous condition, since it is found that drastic treatment such as that applied to the present copolymer by the process of this invention would in general impair the properties of the rubbers. In sharp contrast with this requirement of gentle treatment by all of the prior rubbery materials, the present polymeric substance is greatly improved by a severe milling treatment. This property of substantial improvement in the strength, homogeneity and other characteristics of the olefinic polymers and interpolymers by the application thereto of the above mentioned drastic milling treatment, appears to be unique to these low temperature olefinic interpolymeric bodies. It may be noted that this problem of blistering is unique to the present copolymeric materials. Rubber, (caoutchouc) mixes readily with the desired compounding agents, and cures readily and only deliberate Similarly, the emulsion type of copolymers such as the copolymer of butadiene with styrene known as Buna S and the copolymer of butadiene with acrylonitrile known as Perbunan also do not normally blister during curing reaction; and while all of these materials are commonly treated in the Banbury mill or on the double roll mill, no such blistering phenomena as are encountered with the present copolymer, occurs with them.

It may be noted that standard compounding practice for rubber utilizes both the Banbury mill and the double roll mill for the compounding step and the milling procedure exerts a profound effect upon the substance processed. It is entirely possible to obtain a breakdown of natural rubber in the Banbury mill to the stage where it is little more than a heavy oil. However, rubber, even broken down to this condition, contains enough unsaturation (the iodine number of rubber normally being about 350) so that upon curing, the molecular weight is rebuilt and the firm solid character of the rubber gum restored. This, however, cannot be done with the copolymer of isobutylene and a multi-olefin, since the small amount of unsaturation present makes it impossible to build up the molecular weight if it is too low originally or if it is broken down by any means.

Similarly, polybutene has been compounded in the Banbury or on the double roll mill for the mixing in of various substances, and also for the purpose of breaking down the molecular weight when it is too high for desired use, such as addition to a lubricant. In the case of simple polybutene, however, the material cannot be vulcanized by conventional means and none of the usual vulcanizing agents react with it to increase the tensile strength. Polybutene has been treated with sulfur chloride, to add both sulfur and chlorine to the molecule, but this is a hardening acistics are obtained thereby.

tion, to produce a material much like factice, which does not increase the tensile strength. Furthermore, no question of blistering ever arises with polybutene. In the first place, since it cannot be cured by commercially feasible means, no permanent blisters can be formed in it, but any inclusions of extraneous matter, gaseous, liquid or solid, are easily worked out and removed, and the inherent stickiness prevents the formation of any blisters. Accordingly, milling of polybutene has been, and can be, practiced only for the purpose of mixing in compounding substances, and no question of loss of tensile strength from the presence of blisters can ever arise.

In practicing the present invention, the materials to be processed are prepared by a low temperature polymerization reaction. The raw materials include isobutylene, as the mono-olefinic component.

As the diolefinic component of the mixtures, the preferred substances are butadiene, isoprene, dimethyl butadiene and piperylene. It may be noted that in general, all carbon compounds having from 4 to 14 carbon atoms; and more than one carbon to carbon double linkage; that is, two or more ethylenic linkages in the molecule, are usable, without regard to the relative positions of the double linkages, whether they are conjugated or non-conjugated and without regard to the presence of substituents of any sort. That is, the multiple unsaturated ethers .such as the ether of butadiene and methane or ethane, are entirely satisfactory copolymerizates; similarly, di-al1yl ether is usable as a multiple unsaturated copolymerizate. It may be noted that the preferred copolymerizates are the substituted butadienes containing a methyl group on the 2 carbon, since these compounds copolymerize with the most smoothness and ease; and the condition of conjugation appears to be, in some ways, helpful. However, none of these are essential requirements since butadiene as such is an excellent copolymerizate; 1,4 dimethyl butadiene is a satisfactory copolymerizate; 2,3 dimethyl butadiene being, however, somewhat superior; myrcene also being an excellent copolymerizate.

The mixed olefinic material is cooled to a temperature ranging from l0 to C., preferably to temperatures ranging from -78 C. using solid carbon dioxide to 103 C. when using liquid ethylene. Cooling may desirably be accomplished by the addition directly to the olefinic material of the refrigerant Whether solid carbon dioxide or liquid ethylene or other of the non-reactive refrigerants, such as liquid propane, liquid ethane, or liquid methane. Alternatively, the olefinic material may be cooled by an external refrigerant such as liquid ethylene confined in a suitable refrigerating jacket around a reaction vessel. When an internal refrigerant is utilized, its selection is restricted to those substances which are inert with respect to the catalyst. Such refrigerants as liquid ammonia, liquid sulfur dioxide and the like are not useful as internal refrigerants. However, for external refrigerants, all of these materials are useful, particularly under vacuum, to give lower temperatures than their normal boiling points at atmospheric pressure. The olefinic material may also be diluted with inert diluents, and in some instances advantageous character- Suitable diluents are found in the low freezing alkyl halides such as ethyl, methyl, propyl, or butyl chloride, chloroform, ethylene di-chloride, or in carbon disulfide swim sand-various: other it low 5 freezing? point: incrt sflb- "stances, including a limitednumber oiithetmoderately low-boiling hydrocarbons, such astbutane,

:propane andtthe like.

IiIn:conductinglthe reaction,at purifleda-isoolefln "liquidz-at thetreaotion temperatura rather than r'may preferably be used; thesisoolefln': being-mixed int the proportion of 70 to. 99% uparts iwithi from 'Bmto 1; parts of-the multiolefintwhich mayvpref- *xer'ablyabe ofihigh purity, but: alsmmay becmerely -:.commercial grade, containing from 50'%?to 95%=1zof 2,10 turesxtowyielden interpolymer ofrhigh molecular "the desired diolefin, provided the impuritiesiare u inert substances, 1 such :as the parafilnt; hydrocarbons. '(This mixture may be diluted ifdesirem-and themchille d by the applicationl'oi ther refrigerant,

*merely: liquidfbelow- C., as is? the case with'zthe catalyst solvent.

l'I'he upolymerization "reaction occurswithin a ":very: short: period of "time at 'thesealow tempera- -weight theiaverage viscosity molecular weight. (or WStaudin'ger atmolecular weight number) ranging from 520,000 1; to 5250,000 or' more; the ,upperi'lim it beinglas yet unknown. When the polymerization '"eitherexternalor internal, to temperaturesrhe- L5 --is complete'd, the polymer material is recovered low C., preferably to 'temperatures within the range of +4090. to 103" .C.

'li'he chilled olefinic material is: thenpolymerize'd by f-the application. of the rcatalystyflwhioh,:1ifirlt cation of the catalyst solution mawell-"distrihuted :state 1: such as that produced :by :an atomization israpplied: to the. surface of the rapidly: stirred olefinicmaterial.

:For the "catalyst, any of the Frieda-Crafts iactive-metal halides disclosed by N." 0; ,Callowam in ab volatilization :of "any unpolymerized isoolefln Iorirdiolefln, land by volatilization of i the diluent refrigerantawcatalyst and bylvolatilization or the -;solvent "as well. The amount of catalyst used'zis relatively. very small, and may' be partly removed i by; asimple washingstreatment of the polymer.

As so obtained, the polymer is a coherent mass 'oflmaterialwhichisiwhitein color and-has a good ..:elongation, tbut .does not have an elastic limit,

ifrom a spray nozzle in WhiChhlCflSBfithB :catalyst tbeingplastic under pressure .or tension. Itnis capable of: being cured by a heat treatment with sulfur, or i with an. organic compound containing raquinonoid nucleus of the benzene -=or naphthav-leneseries, *or a dinitroso compound to produce rarticle on the Friedel-Crafts ssynthesisi 1330 :aimaterial which does have an elastic limitgaiid iprinted insthetissue of ChemicaLReViewsgrpub- -lished for the American .Chemical 3. Society vi at 'Baltimoreiin 1935,. in-vo1umeXVII, No. 3,?"Lthe article beginningon page .327, the ,liStfbBiIlEQflf- =ticular1y well shown onpage :3'75"may bensed.

the solvent t be xrnon-complexeforming :and lowfreezing. To be low-freezing; it: is .merelyznecessaryithat the solvent. have .a. boiling: pointibelow salsotaz-good abrasionand flexure resistance.

:It. is to be noted that this polymeric material sis 1a low "unsaturation, linear ltype' hydrocarbon eorroleflnic hydrocarbon havingan :iodinevnumber i'rangingf from lito orf60, depending upon. the iiFor in the catalyst solvent, 1 it is i necessary: that :amount ofndiolefin copolymerized into the;polyt mer. This very low iodine number. is; in contrast withtthe iodine number of the original isobutylene which is approximately 450, and with the iodine 0 6C. (below the freezing pointotwater). Tosbe unumber of" butadiene or isoprene monomer, in

'non-complex-forming, itis merely necessaryathat there. shall not separate fromi the nsolutioneon evaporation :of the solvent 1.8, compoundmetween thetsolventrand the Friedel-Grafts.catalyst; or

;either of which it is -approximately 900, an'd'in xcontrastwithrubber which has an iodine number -of=approximately 350to 370. This outstanding -diference in iodine number is significant in. that .that the addition of the solventain tthe 11 form lt shows-conclusively that the material isnotiaan of vapor .to the solute at constant: temperature will lead to a substantially continuous change in ithecomposition of the catalyst phase and to a. rcontinuousincrease in the partial pressure ofrthe artificial'rubber, but is a wholly difierent sub- "-stance beingva: low 'unsaturation polymer ras dis- :tinguishedr from the highly unsaturatedenatunal -mbberx. substances. Furthermore, while the in- :solvent. In general,- the catalyst'ca'n be recovered 1550 i terpolymeric 'material :reacts with wisuliur, :the

unchanged by "removal of the solvent (Findlay, The Phase Rule and Its Application, fith'edition, Longmans GreenSr Company, NewYo'r-k). For .thecatalyst solvent, such substancestas methyl reaction isvdifierent from that of sulfurizingrubtber; since thetvulcanizationias it occurs in: rubber Hie-dependent upon the high degree of unsatura- Etion: of the rubber, and, the sulfur serves. tosatuchloride, ethyl chloride, carbon disulfide, methirateia"portionconly .of the .double bondslins-the ,,y1ene dichloride, ethylene dichloride, chloroform,

utertiary butyl chloride and various of thelower hydrocarbons are useful. Any solvent capable of dissolving up to0105% ofthe active"hali de rubberpwhereas the olefinic polymer here disvclosed: is. nearly 1 completely saturated, :but xtvill -absorbssuliur, which wcan be a combined :with the Mew :Jdouble irbonds which .produce 'the .small .z-catalyst under conditions designedlto .avoid'de- 5260d amountc.oftunsaturation present.

inc'properties. ,For the diluent:-suchwsubstanoes ,ias methyl chloride;,methyl bromide etheylzchloride, methylene :dichloride. ethylene tqdichloride,

*chioroform; carbon disulfidenon the rlowera hydrotcarbons which are liquid at the reactionftempeta- ".1135 =s11bstances are I nu n ne re xq none inoreFor the ouring L: agent, various substances: sate :available. The principal curing agent is 'elevmentalcsuliur, .1preferably. in the presence; of H311, l appropriate sulfurization aid such as tetramethyl sthiuramidisulfide or. selenium: tetra ethyl dithio- @ca'rbamate, :or tetra; methyl thiuram mono sulfide, rzzinc dimethyldi thiocarbamate, or zinc dibutyl izdithio'carbamate, or di penta methylene thiuram atetra" sulfide. :These substances are representa- ,.since2the resultin polymerntends towbesuperior 1770 .tive of zarsconsiderable list of sulfurizationtaids wwhich .arermore or'less ellectivein reducing the -curing time.

Alternatively, 1 theaquinone dioxime-substances may he: need, Tests have shown that preferable .ganic salts. curing effect without the presence of sulfur.

,the like. ing effect can be obtained by any dinitroso comor the various dinitroso compounds.

. or ,dinitroso compounds.

These compounds yield an excellent The exact method of operation is still unknown but apparently these compounds produce a crosslinkage between adjacent copolymer chain molecules, the exact reaction, however, being uncer tain.

Similarly useful are the dinitroso compounds such as dinitroso cymene, dinitroso benzene, and

Tests have shown that a valuable curpound, whether aromatic or aliphatic, although,

,of course, there is a difference in the efiiciency and speed of curing; a difference in the obtainable tensile strength, and a difference in the cost It may be noted further that only the meta and para forms of the aromatic quinones and dinitroso com- -.pounds are stable, since the orthocompounds tend strongly to form secondary rings and therefore other compounds which are not dioximes In the commercial production of these copolymers, they are usually produced in continuous apparatus in which a stream of mixed olefins and diluent is delivered to a refrigerant jacketed reactor with an auxiliary stream of catalystsolu- .tion, the contents of the reactor being powerfully stirred and circulated. The continuing streams result in a continuing overflow of solid polymer, slurried in a mixture of unreacted ,unsaturates,

diluent (if used) and catalyst solvent. This overfiw is usually discharged into a tank of warm ;water to volatilize out everythingbut the solid polymer and convert the slurry of polymer -in hydrocarbons into a slurry of polymer in water.

This water slurry is then strained, -or filtered,

and passed through a drying oven to remove as much as possible of the moisture.

The polymer, after separation from the water slurry and drying, is then ready for the heavy ;mil1ing treatment of the present invention. The

essence of the present invention is the application to the polymer of a heavy mechanical work ing treatment at an elevated temperature sufficient to destroy the blistering tendency.

As above pointed out, this heavy mechanical working is conveniently applied in the Banbury type mill, the milling being conducted at temperatures between about 150 C. and.200 C. for

time intervals ranging from 5 minutes to 30 minutes, the length of time usually being inversely proportional to the temperature. Alternatively, the milling may be conducted upon the standard double roll mill, again at temperatures within the range between 150 C. and 200 C. for time intervals ranging from 5 to 30 minutes. It may be noted that the heavy pressures are indicated by the pressure required to produce a 50% reduction in thickness of the polymer layer on the front roll in the double roll mill and it appears that the Banbury treatment applies similar pressures.

'Alternatively, the ordinary Werner and Pfleiderer type of kneading machine may be used, although are usually required. Alternatively, also, mecha- -nism of the taffy-pulling type may also be used.

However, this requires a preliminary milling and plasticizing step and the use of auxiliary heating equipment and it is therefore less desirable commercially. Other means for applying heavy working treatment to the copolymer will be evident to those skilled in the art; the essence of the invention being the application tothe polymer of heavy mechanical working at temperaundesirably high temperatures and time lengths agents are mixed in.

-- reaction and the delivery to the mills.

8 -tures within the range between 150 C. and 200 C. for time intervals between 5 minutes and 30 .minutes.

It may be noted that this heavy milling step :iiS preferably applied to the polymer before any of the compounding and curing ingredients are .addedand is necessarily applied before the curing The presence of compounding agents is somewhat undesirable since they may tend to complicate the milling problems and lengthen the time required for the desired results. The curing agents must be absent from j'themixture during the heavy milling step since otherwise the material will scorch and setup on the. mill in a vulcanization reaction which .de- 'stroys the usefulness of the polymer.

The milling step may, if desired, be conducted upon the polymer as it is received from the dryers, -without the presence of an auxiliary agents.

This, however, is less satisfactory than a treat- 'ment in the presence of a stabilizer such as phenyl eta naphthyl amine or ZA-di-tertiary butyl para .lcresol, or triphenyl phosphite, or the like in concentration ranging from 0.05% to 1% or 2%,. It may be noted that the heavy milling treatment tends to yield a slight molecular weight breakdown in the polymer. If, as is sometimes the case, the molecular weight from the polymerizer is high enough to make the material leathery and hard to, process, this incidental breakdown is helpful. If, on the other hand, the molecular weight, as received from the polymerizers, is about right for convenient processing, any further breakdown is avoided by the use of an inhibitor of the above-mentioned type. When the polymer- .izers are operating satisfactorily, it is usually possible to forecast the character of the polymer to be obtained, and add an appropriate amount of inhibitor; since, however, the inhibitor is also valuable for protecting the polymer during storage, before curing, it is usually added at some convenient stage between the primary polymerization When the heavy milling step is completedythe polymer is ready for compounding and curing. A suitable compounding recipe is as follows:

Parts Copplymer stearic acid 0 to 10 Zinc oxide "0 to 10 Carbon black 0 to 200 Curing agents 0.5 to 5 This recipe shows the usual range of ingredients; A specific desirable recipe is: j I Parts fCopolymer (3 molecular per cent isoprene') 1 00 .Stearic acid 5 Zinc oxide 5 Carbon black 50 Sulphur 3 Tetra methyl thiuram disulfide 1 110 Crbeforestheaccelerator is added sincew otherwise :thepolymer-a tends to set up onthe mill.

After. the compounding step, the polymer:

is given the usual forming treatmentsuch as by molding; orycalenderinglontofabricor other processes anditlis thereafter cured. The curing re. action is usually-conducted .at temperatures ranging irom3illl-to 3503 FL, depending.upontheproduct beingmade, thecharacter ofithecuring agent,

and otherfactors, fora timewithin the rangebee tweenthreeminutes and, twohours, depending... upon the, curing agents used, and the use. to. be

made Of-the cured material.

Example 1 I The present invention introduces into the treatment of the polymer a: particular type of processing step. When-1 the' polymerization reaction has been completed and the volatile solvents rea moved, and preferably also the catalyst had been removed, the polymer material is introduced "into aiBanbury. type of mixer, and milled in the Banbury mixer at a,temperature ranging r between? 150 C.,and200 C., for a periodorfrom 5 to-30i' minutes; At-such temperatures the polymeric material has a. high degree of plasticity; an-diunder the mixing and compressive forces developed in the Banbury mill a homogenization of the polymer'materialhccurswhich greatly improves the physical characteristics of the polymer after it has 'b'eencured. In sharp contrast with other rubbery'materials; no substantialchange inmoleculariweight is produced by: the milling treatment,

but instead the materialretains substantially the original=molecular Weight; and does not sustain anydegradation in molecular weight, nor any increase-in plasticity but does obtain a .veryrimportant gain inmltimate tensile strength after curing-r 'Iherexact function of this specific treatmentis as=yet unknown butit seems probable thatln the} course, of the polymerization reaction a small amount, probably; only, atfraction or 1%, of' polymeric material; otrelatively lowmolecular-weight is produced. This, material, if it'ismproducedp, is of sufficiently low molecular weight to be physicala ly in the form of a very viscous oil, rather than in the form of the solid elastic material which is the form, taken by the remainderof the polymer material. It may also be that this oily polymer.

material is slightlyvolatile or unstable at thecuring: temperature, perhaps sufiiciently volatile or unstable to develop small bubbles within the body of the composition, It further seems probable that this material, if produced, occurs in segregated small droplets withinthe body-of the polymer; perhaps beingwproduced atsome 'particularx stage of thepolymerization reaction, and perhaps produced at some critical local concentration of catalyst, diluent and mixed olefinic materials in.

at the high temperature dispersesthe droplets on oil, polymer uniformly throughout :the, mass of 10 polymeric, material, thereby destroying any local comparatively high concentration which might otherwise be sufficiently great to produce bubbles. Alternatively, it may;:be that the milling operation,.atthigh temperature volatilizes and drives offer-chemicallyreacts with part-at least of any troublesome; low molecular weight, oily constituents which imay bespresent, The above theories are. advanced, as, tentative. suggestions of POSSi-r l ;b18- reasons for the; improvement discovered by the treatment; but have :not as yetibeen provcn.

In anyrevent,v this isoolefinic type. of polymer is greatly; improved inits. physical characteristics by-aqtreatment of:such severity asto :be detri-m 1 mental :tori-theaphysical propertiesrof other comparable substances:- such as natural rubber or syntheticyrubberss.all10f whichare harmed by:

suchorastic treatmentboth as to theseverity of the pressure; the temperature and the prolonged" timeof application of temperature and milling pressure:

When. the milling in l the Banbury mixer has been completed, the -material may be removed from the mill-and"allowedto cool.

tensile-strength;

Emmplea 2 s 'ilhevalueof ,hot milling as; a means ofstabiliz ing, the interpolymersl of the present invention tocprevent deterioration during storagecwass cs1 l tab1ished,.-f0n a p eriod overrthree months;

BOZ IGnrcat 155 0;.

Descriptionpf Sample Tensile gi JTensile' long; I

Butadiene isobutylene. interpolymel" original f evaluation (aiten'Be ry Tre m t).

Butadienc-isobutylene interpolymenafteriBanr bury Treatment. (a). followed "by aging (b):

Butadicnc-isobutylenc interpolymcr. after, modified -Ban-bury" treatment. L(c) foll lwedg 1 byas ed lfl n uu Butadiene-iscbutylcne intcnpolymem aged; without Banbu'ry Treatment (b) followed by; Banhury- Treats- 1 ment, and, standard: evaluation;

Blistercd (1.5 parts),zinc oxide (all-parts); and stcaric aci l (3 parts).

(b), ,Shelfagingfol, 33/; months (c)--l00 parts Banburicd -ZO minutcd at l-140 O. with sulfur (1.5 parts) only."

These-values showthedeterioration of the interpolymerupon storage in the absence of a pro-- liminary milling;- treatment; and showthe excellent retention- -of tensile strength and elongation when" the' milling treatment is applied. soon after the polymerization step.

As above pointed out; this .milling, or Banbury treatment stepyis applicable" to; all of' the predominantly, isoolefi'nic copo1ymers;if they are solid; andjreactive in a curing reactionh 1171383 alternative; embodiment, a olymerize, tion; mixture? was; prepared comprising purified.

It may then becompounded;extrudedand'cured at the user's convenience *without the developmentof blisters or other difficulties which-reduce the obtainable;

Cure at '0.

Per Cent and isoprene in the proportion of parts to part. As above pointed out, this mixture was preferably prepared from isobutylene of a maximum purity, containing as little of the normal mono-olefins as possible. The material contained non 1 96% to 99.5% of isobutylene. The isoprene may be of a high degree of purity, or the material used may contain from 50% to 95% of isoprene, the remainder being inert impurities. This mixture was chilled as before to temperatures ranging from 50 C. to 150 0., diluted with a diluent-refrigerant such as liquid ethylene or liquid propane and solid carbon dioxide or other suitable refrigerant composition. The mixture was then polymerized by the addition of the Friedel-Crafts type catalyst solution as before. This polymerization procedure produced a copolymerizate which was closely similar to the previously described copolym'erizate, in that it could be milled as above described and compounded with sulfur and cured to develop an elastic limit, and high tensile strength, high elasticity, high abrasion and fiexure resistance, all of which are influenced by the milling treatment.

Various portions of the polymer material as above produced were compounded with sulfur and a sulfurization aid, some with and some without filler substances, others with organic quinonoid nucleus compounds of the benzene and naphthalene series, including para-quinone dioxime both with and without an oxidizing agent such as lead peroxide, and when so compounded the compound was cured by heat, whereupon there was developed in the cured material a definite elastic limit, a high elasticity and a high tensile strength as Well as the above-mentioned high resistance to flexure and abrasion. The sulfur curing reaction required a relatively high temperature, and a relatively long time of reaction. With sulfur alone, the temperature required was in the neighborhood of 160 C. and the time was four or more hours. The Banbury treatment was desirably conducted at a slightly lower temperature for a substantially shorter length of time, and accordingly the sulfur may safely be added to the polymer mixture during the course of the Banbury treatment. It was found, however, that the sulfurization and curing were greatly facilitated by the presence of one or more of a specific group of compounds, that is, the v thiuram compounds such as tetramethyl thiuram disulfide. The presence of approximately 1% of this sulfur-containing substance increased the rate of cure to such an extent that it was completed in from 15 to 30 minutes at a temperature ranging from 140 C. to 170 C. In view of these facts, it is desirable that the organic sulfur compound of the group above mentioned should not be added to the hot polymer either with or Without additional filler substances. Instead it is desirable that the sulfurization aid be added only after the material has been considerably cooled, and that it be added with the minimum amount of further milling at elevated temperatures. It is found, however, that the sulfurization aiding compound above-mentioned may safely be added to the polymer material on the mill by adding it when the material has been cooled to or below a temperature of 110 C. if the milling at this temperature does not continue for longer than approximately 5 minutes.

Alternatively, of course, the material may be removed from the Banbury mill after the milling treatment and cooled in any convenient Way. Thereafter, it may be stored as desired, and when ready for curing, the sulfurization aid may be incorporated by short working in a relatively cool A convenient and desirable formula for producing a compounded polymeric material is as follows:

Parts Isobutylene-isoprene copolymer Zinc oxide 5 Stearic acid 3 Sulfur 3 Tetramethyl thiuram disulfide, added after milling to the cold, milled, product 1 This material mixed in a cool Banbury mixer or upon an ordinary roll mill blisters badly and cannot be properly cured.

If the polymer alone is milled in the Banbury (for example, 25 minutes at C.) and then the compounding materials added and mixed in with the minimum of further milling and at a lower temperature, the material can be cured with only occasional blisters or bubbles and the material is generally'satisfactory. If the polymer is mixed in the Banbury mill with the fillers (zinc oxide and stearic acid) at a temperature of, for example, 160 C. for 25 minutes, then cooled and the sulfurization aid mixed in, the material is of phenomenally high grade and Shows a, tensile strength in the neighborhood of 3,460 pounds per square inch with an elongation of 980%.

This procedure may conveniently be, sum

marized in the following table:

Material Resultslggngd) 1 hr. at

#1. Conolymeric material mixed with all compoundingand vulcanizing ingredients 3% stearic acid, 3% sulfur, 5% zinc oxide and 1% 'luads.

#2. Polymeric material kneaded in Banbury alone for 25 minutes at impossible properly).

to sulfurize Can be cured with only occasional blistering (but 160 C. then mixed on mill with generally satisfactory). all compounding ingredients.

#3. Treated in Banbury at 160 C. with sulfur, stearic acid and zinc oxide, after treatment and cooling, accelerators are milled in.

sq. in. Elongation 980%.

1 Good results are often obtained by Banbury treating with any one or any combination of the compounding ingredients. However, the most satisfactory results are obtained by using all three.

Note: By the method of item #1 above the tensile strength cannot ordinarily be determined due to flaws, blisters, etc., whereas, by the method in item #2, the tensile strength was 2700 lbs/sq. in. This value is satisfactory for some purposes and therefore this method can be employed. However, for maximum tensile strength the method in item #3 is preferred.

The polymeric materials when treated in accordance with the present invention are highly advantageous substances for the wide variety of uses where strong, elastic material is required,

such uses including automobile tires and tubes,

waterproof and chemical-proof fabrics, and elastic bodies generally.

It will be observed that two different kinds of Blisters badly (generally Tensile strength 3460 lbs.

meanness m-ill machinery-rarer mentioned; thewBanliury-smills. and the open mill.

An: open mil 1 consistsaofutwoparallel steel rollers rotatingzaimopposite .directions, one revolving slightlywfasterzthanthe. other: A Banbury mixer is an enclosed kneader-type mill with specially designed blades to-d-uplicate the shearing action of the. open mills. In this .typeiof mixerithearea exposed to the atmosphere iscomparatively,

small. hence, the polymer being worked is not exposed to so muchoxygen as occurs-with the open mill. In addition, the rotorsaand the jacket oti the Banbury :mill can be heated by-passingsteani through them to.produce..the.,.desired high temperature for the milling operation.

TheiBanbury mill is superiorito the opemmilly for r the 5 drastic .milling treatments above pointed out, because-pf the muchx; more: severet. milling forces applied, and because of the much less opportunity for the access of atmospheric oxygen to the material. However, similar results can be obtained by high speed working on an open mill with very hot rolls.

Thus the invention provides a new and useful step in a process for the production of synthetic plastics whereby the tensile strength, storage stability characteristics and other properties are valuably improved, by a treatment of a severity which is ordinarily injurious to the valuable characteristics of other reactive plastic and elastic materials.

This application is a continuation in part of application Serial No. 272,610, filed May 9, 1930, and application Serial No. 431.586, filed February 19, 1932, both now abandoned.

While there are above disclosed but a limited number of embodiments of the structure of the invention, it is possible to produce still other embodiments without departing from the inventive concept herein disclosed, and it is therefore desired that only such limitations be imposed upon the appended claims as are stated therein or required by the prior art.

The invention claimed is:

1. In a process for preparing a solid plastic curable hydrocarbon interpolymer of a major proportion of isobutylene with a minor proportion of an aliphatic multi-olefin having from 4 to 14 inclusive carbon atoms per molecule at a temperature within the range between 40 C. and -164l C. in the presence of a polymerization catalyst comprising a Friedel-Crafts active metal halide in solution in a low freezing non-complex forming solvent, the step of milling the curable polymer in the absence of a vulcanization aid at a temperature within the range between 150 C. and 200 C. for time intervals from 5 minutes to minutes under milling pressures great enough to effect a rapid breakdown of caoutchouc and thereafter curing the polymer in the presence of a vulcanization aid, the milling step serving to prevent the development of blisters upon subsequent curing.

2. In a process for preparing a solid plastic curable hydrocarbon interpolymer of a major proportion of isobutylene with a minor propor-- tion of an aliphatic multi-olefin having from 4 to 14 inclusive carbon atoms per molecule at a temperature within the range between C. and -16 C. in the presence of a polymerization catalyst comprising aluminum chloride dissolved in methyl chloride, the step of milling the polymer in the absence of a vulcanization aid at a temperature within the range between 150 C. and 200 C. for time intervals from 5 minutes to 30 Eminutestunderirmillingi pressures greatvenough to; effect: as rapidibreakdowm of caoutchouc 1* and. thereafterrcuringitheepolymer: in the presence-off.

a avulcanizatiom aid? the :rmilling, step; serving to prevent therdevelopmentiof blisters upon subsequenticuringu In. as. process; for preparing a solid plastic. curablehydrocarbon interpolymery of? a majorii" proportioniof: isobutylene: with a minor; propor-i artemperatureyxwithin;the1 range between C.

andx200 C. tion time; intervals from 1 5 minutes tos 30 minutes under milling pressures great enough to effect a rapid breakdown of caoutchouc, the milling step serving to prevent the development of blisters upon subsequent curing; thereafter compounding the milled polymer with a curing agent and curing the compounded polymer by heating to a temperature within the range between 235 F. and 350 F. for a length of time within the range between 3 minutes and 2 hours.

4.. In a process for preparing a solid plastic curable hydrocarbon interpolymer of a major proportion of isobutylene with a minor proportion of an aliphatic multi-olefin having from 4 to 14 inclusive carbon atoms per molecule at a temperature within the range between -l0 C. and 16l C. in the presence of a polymerization catalyst comprising aluminum chloride dissolved in an alkyl chloride having from 1 to 4, inclusive, carbon atoms per molecule, the step of milling the curable polymer in the absence of a vulcanization aid at a temperature within the range between 150 C. and 200 C. for time intervals from 5 minutes to 30 minutes under milling pressures great enough to effect a rapid breakdown of caoutchouc and thereafter curing the polymer in the presence of a vulcanization aid, the milling step serving to prevent the development of blisters upon subsequent curing.

5. In a process for preparing a solid plastic curable hydrocarbon interpolymer of a major proportion of isobutylene with a minor proportion of butadiene at a temperature Within the range between -40 C. and 164 C. in the presence of a polymerization catalyst comprising aluminum chloride dissolved in methyl chloride, the step of milling the curable polymer in the absence of a vulcanization aid at a temperature within the range between 150 C. and 200 C. for time intervals from 15 minutes to 30 minutes under milling pressures great enough to effect a rapid. breakdown of caoutchouc and thereafter curing the polymer in the presence of a vulcanization aid, the milling step serving to prevent the development of blisters upon subsequent curing.

6. In a process for preparing a solid plastic curable hydrocarbon interpolymer of a major proportion of isobutylene with a minor proportion of isoprene at a temperature within the range between 40 C. and 164 C. in the presence of a polymerization catalyst comprising aluminum chloride dissolved in methyl chloride, the step of milling the curable polymer in the absence of a vulcanization aid at a temperature within the range between 150 C. and 200 C. for time intervals from 5 minutes to 30 minutes under milling pressures great enough to efiect a rapid breakdown of caoutchouc and thereafter curing the polymer in the presence of a vulcanization aid, the milling step serving to prevent the development of blisters upon subsequent curing.

'7. In a process for preparing a solid plastic curable hydrocarbon interpolymer of a major proportion of isobutylene with a minor proportion of dimethyl butadiene at a temperature within the range between 40 C. and -164 C. in the presence of a polymerization catalyst comprising aluminum chloride dissolved in methyl chloride, the step of the milling the curable polymer in the absence of a vulcanization aid at a temperature within the range between 100 C. and 200 C. for time intervals from 5 minutes to 30 minutes under milling pressures great enough to efi'ect a rapid breakdown of normal polymer and thereafter curing the polymer in the presence of a vulcanization aid, the milling step serving to 16 prevent the development of blisters upon subsequent curing.

IRVING E. LIGI-ITBOWN. WILLIAM J. SPARKS. ROBERT M. THOMAS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,276,893 Thomas Mar. 17, 1942 FOREIGN PATENTS Number Country Date 482,547 Great Britain Mar. 28, 1938 482,573 Great Britain Mar. 28, 1938 

1. IN A PROCESS FOR PREPARING A SOLID PLASTIC CURABLE HYDROCARBON INTERPOLYMER OF A MAJOR PROPORTION OF ISOBUTYLENE WITH A MINOR PROPORTION OF AN ALIPHATIC MULTI-OLEFIN HAVING FROM 4 TO 14 INCLUSIVE CARBON ATOMS PER MOLECULE AT A TEMPERATURE WITHIN THE RANGE BETWEEN -40*C. AND -164*C. IN THE PRESENCE OF A POLYMERIZATION CATALYST COMPRISING A FRIEDEL-CRAFTS ACTIVE METAL HALIDE IN SOLUTION IN A LOW FREEZING NON-COMPLEX FORMING SOLVENT, THE STEP OF MILLING THE CURABLE POLYMER IN THE ABSENCE OF A VULCANIZATION AID AT A TEMPERATURE WITHIN THE RANGE BETWEEN 150*C. AND 200*C. FOR TIME INTERVALS FROM 5 MINUTES TO 30 MINUTES UNDER MILLING PRESSURES GREAT ENOUGH TO EFFECT A RAPID BREAKDOWN OF CAUTCHOUC AND THEREAFTER CURING THE POLYMER IN THE PRESENCE OF A VULCANIZATION AID, THE MILLING STEP SERVING TO PREVENT THE DEVELOPMENT OF BLISTERS UPON SUBSEQUENT CURING. 